1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor film, and more particularly, to a method for manufacturing a semiconductor film which is suitable for use as a solar cell or a silicon-on-insulator (SOI) substrate.
2. Description of the Related Art
Recently, a technique for manufacturing an SOI substrate has been attracting notice as a technique for improving the processing speed of a semiconductor device and allowing saving of electric power. The SOI substrate is obtained by forming a semiconductor film having a thickness of about several tens of nm to a few xcexcm, for example, a single-crystal silicon film, on an insulating layer. Methods for inexpensively manufacturing a solar cell using such a thin semiconductor film have also been proposed.
U.S. Pat. No. 5,856,229 describes a method for manufacturing such an SOI substrate. In this method, first, a first substrate (wafer) comprising nonporous single-crystal silicon is prepared, and a porous silicon layer is formed by anodizing a surface of the first substrate. Then, a nonporous single-crystal silicon layer is formed on the porous silicon layer according to epitaxial growth. An insulating layer comprising silicon oxide is formed by oxidizing the surface of the nonporous single-crystal silicon layer, and a multilayer structure is formed by bonding a second substrate on the surface of the insulating layer. Then, an SOI substrate is manufactured by separating the nonporous single-crystal silicon layer from the first substrate at the porous silicon layer by applying an external force, such as a tensile force or the like, to the multilayer structure, and transferring the nonporous single-crystal silicon layer onto the second substrate via the insulating layer.
U.S. Pat. No. 6,054,363 describes another method for manufacturing an SOI substrate. In this method, the same processing as described above is performed until a multilayer structure is formed. After this processing, the nonporous single-crystal silicon layer is separated from the first substrate by applying an abrupt thermal stress to the porous silicon layer, by heating the nonporous single-crystal silicon layer by causing a current to flow only therein.
It is an object of the present invention to provide a method for manufacturing a semiconductor film more simply and efficiently by improving the above-described conventional methods.
According to one aspect of the present invention, a method for manufacturing a semiconductor film includes the steps of preparing a first member including a semiconductor substrate, a semiconductor layer, and a separation layer provided between the semiconductor substrate and the semiconductor layer, bonding or attracting a second member which is hardly heated by induction heating, onto the semiconductor layer of the first member, and separating the semiconductor layer from the semiconductor substrate at the separation layer by heating the semiconductor substrate by induction heating.
According to another aspect of the present invention, a method for manufacturing a semiconductor film includes the steps of preparing a first member including a semiconductor substrate, a semiconductor layer, and a separation layer provided between the semiconductor substrate and the semiconductor layer, bonding or attracting a second member whose resistivity is higher than a resistivity of the semiconductor substrate, onto the semiconductor layer of the first member, and separating the semiconductor layer from the semiconductor substrate at the separation layer by heating the semiconductor substrate by induction heating.
According to still another aspect of the present invention, a method for manufacturing a semiconductor film includes the steps of preparing a first member including a semiconductor substrate, a semiconductor layer whose resistivity is higher than a resistivity of the semiconductor substrate, and a separation layer provided between the semiconductor substrate and the semiconductor layer, and separating the semiconductor layer from the semiconductor substrate at the separation layer by heating the first member by induction heating. It is desirable that the resistivity of the semiconductor layer is at least 10 times the resistivity of the semiconductor substrate. It is desirable that the resistivity of the semiconductor layer is at least 1 xcexa9xc2x7cm, and the resistivity of the semiconductor substrate is equal to or less than 0.1 xcexa9xc2x7cm.
In the present invention, the first member is prepared by a step of forming a porous silicon layer, serving as a separation layer, by anodizing a surface of a nonporous silicon substrate, and a step of forming a nonporous silicon layer on the porous silicon layer according to epitaxial growth. (3) The first member may also be prepared by a step of forming an ion-implanted layer, serving as a separation layer, except for a silicon layer where ions are not implanted on a surface thereof, by implanting at least one type of ions selected from hydrogen, nitrogen and helium to a predetermined depth from a surface of a silicon substrate. In this process, a protective film may be formed on the surface of the silicon substrate before implanting the ions.
In the present invention, the step of heating the semiconductor substrate by induction heating is performed by mounting the bonded or attracted first and second members on an induction-heating mount around which a coil is wound, and causing a current to flow in the semiconductor substrate by supplying the coil with a high-frequency current. Slits may be formed in the separation layer before heating the semiconductor substrate by induction heating. A tensile force, a compressive force or a shearing force may be applied simultaneously with the induction heating. A pressure or a hydrostatic pressure by a fluid may be applied to the separation layer simultaneously with the induction heating. The second member may be cooled simultaneously with the induction heating.
After separating the semiconductor layer, a residue of the separation layer remaining on the semiconductor layer is removed according to etching, if necessary. After separating the semiconductor layer, a remaining semiconductor substrate may be reutilized for preparing another first member. At that time, a residue of the separation layer remaining on the semiconductor substrate may be removed according to etching, if necessary.
According to yet another aspect of the present invention, a method for manufacturing a solar cell includes the steps of forming a porous silicon layer by anodizing a surface of a p+-type nonporous silicon substrate, sequentially forming a pxe2x88x92-type nonporous silicon layer and an n+-type nonporous silicon layer on the porous silicon layer according to epitaxial growth, attracting an attraction mount which is hardly heated by induction heating, on the n+-type nonporous silicon layer, separating the pxe2x88x92-type and n+-type nonporous silicon layers from the p+-type nonporous silicon substrate at the porous silicon layer by heating the p+-type nonporous silicon substrate by induction heating, and forming electrodes on the separated pxe2x88x92-type and n+-type nonporous silicon layer.
According to yet a further aspect of the present invention, a method for manufacturing an SOI substrate includes the steps of forming a porous silicon layer by anodizing a surface of a p+-type nonporous silicon substrate, forming a pxe2x88x92-type nonporous silicon layer on the porous silicon layer according to epitaxial growth, forming a silicon-oxide layer on a surface of the pxe2x88x92-type nonporous silicon layer, forming a multilayer structure by bonding another nonporous silicon substrate on a surface of the silicon-oxide layer, and separating the pxe2x88x92-type nonporous silicon layer from the p+-type nonporous silicon substrate at the porous silicon layer by heating the multilayer structure by induction heating.
The foregoing and other objects, advantages and features of the present invention will become more apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.